Scientific and technological interest in graphene has rapidly grown recently because of the extraordinary electronic properties of the two-dimensional material. (See, Geim, A. K. Science 2009, 324, 1530-1534.) The mean free path for electron-phonon scattering in graphene is astonishingly long (>2 mm), and as a result, the room temperature electronic mobility in graphene could potentially exceed 200,000 cm2 V−1 s−1 if scattering from disorder in the extrinsic environment were to be minimized. (See, Morozov, S. V.; Novoselov, K. S.; Katsnelson, M. I.; Schedin, F.; Elias, D. C.; Jaszczak, J. A.; Geim, A. K. Phys. Rev. Lett. 2008, 100, 016602; Chen, J. H.; Jang, C.; Xiao, S. D.; Ishigami, M.; Fuhrer, M. S. Nat. Nanotechnol. 2008, 3, 206-209.) Next-generation, ultrahigh performance electronics and transistor logic circuits are envisioned that exploit these exceptional properties. (See, Wang, X. R.; Ouyang, Y. J.; Li, X. L.; Wang, H. L.; Guo, J.; Dai, H. J. Phys. Rev. Lett. 2008, 100, 206803.) Other potential electronic applications of graphene as transparent conductors, sensors, and in flexible electronics have also been demonstrated and proposed. (See, Kim, K. S.; Zhao, Y.; Jang, H.; Lee, S. Y.; Kim, J. M.; Ahn, J. H.; Kim, P.; Choi, J. Y.; Hong, B. H. Nature 2009, 457, 706-710; Schedin, F.; Geim, A. K.; Morozov, S. V.; Hill, E. W.; Blake, P.; Katsnelson, M. I.; Novoselov, K. S. Nature Mat. 2007, 6, 652-655.)
Unfortunately, however, despite its excellent charge transport characteristics, the applicability of graphene in many electronic applications is currently limited because graphene does not have a technologically significant band gap >>kT. (See, Castro Neto, A. H.; Guinea, F.; Peres, N. M. R.; Novoselov, K. S.; Geim, A. K. Rev. Mod. Phys. 2009, 81, 109-162.) The insufficient band gap limits how strongly the conductance of graphene-based devices can be modulated by extrinsic or field-effect doping—which is a critically important behavior for semiconductor applications.
To address this problem, it has been shown that quantum confinement effects can be used to open up a band gap in graphene. For example, it has been demonstrated that the band gap of graphene nanoribbons, Eg, patterned using electron-beam lithography, roughly varies inversely with the width of the nanoribbons, w, according to Eg˜0.2-1.5 eV-nm /w. (See, Castro Neto, A. H.; Guinea, F.; Peres, N. M. R.; Novoselov, K. S.; Geim, A. K. Rev. Mod. Phys. 2009, 81, 109-162; Stampfer, C.; Gutttinger, J.; Hellmueller, S.; Molitor, F.; Ensslin, K.; Ihn, T. Phys. Rev. Lett. 2009, 102, 056403; Yang, L.; Park, C. H.; Son, Y. W.; Cohen, M. L.; Louie, S. G. Phys. Rev. Lett. 2007, 99, 186801.) Other forms of nanostructured graphene showing semiconducting behavior have also been fabricated using electron-beam lithography, including graphene quantum dots. (See, Ponomarenko, L. A.; Schedin, F.; Katsnelson, M. I.; Yang, R.; Hill, E. W.; Novoselov, K. S.; Geim, A. K. Science 2008, 320, 356-358.) and inverse dot (See, Eroms, J.; Weiss, D. arXiv:0901.0840; Shen, T.; Wu, Y. Q.; Capano, M. A.; Rokhinson, L. P.; Engel, L. W.; Ye, P. D. Appl. Phys. Lett. 2008, 93, 122102.)
The successes of electron-beam lithography in fabricating graphene nanostructures that exhibit semiconducting behavior have highlighted two future challenges. First, in order to open a band gap >>kT in nanostructured graphene, it must be nanopatterned to critical dimensions <20 nm. However, 20 nm is on the threshold of what can easily be achieving using conventional electon beam lithography due to known electron scattering effects in common electron-beam resists. More recently with an experimental electron beam resist system features down to 10 nm have been demonstrated. (See, Miyazaki, T.; Hayashi, K.; Kobayashi, K.; Kuba, Y.; Ohyi, H.; Obara, T.; Mizuta, O.; Murayama, N.; Tanaka, N.; Kawamura, Y.; Uemoto, H. J. Vac. Sci. Technol. B 2008, 26, 2611.) However the second challenge is that, electron-beam lithography is a serial technique, which limits its throughput and applicability to the large-area patterning of graphene. Thus, in order to more practically realize nanostructured graphene-based materials, new patterning techniques that can be extended to large-areas with sub-20 nm resolution are needed.